Transcranial magnetic stimulation (TMS) is widely used as a research tool to study aspects of the human brain and has recently been used as a tool in therapeutic neuropsychiatry.
Biological tissue can be stimulated using magnetic fields produced by passing electrical currents through electrically conductive materials positioned adjacent to the tissue. The magnetic fields are intended to induce an electric field in a tissue, provided that the tissue is a conductive medium. More specifically, magnetic stimulation can cause electric conduction in brain cells, and, as a consequence, generation of action potentials.
The magnetic stimulation is delivered or generated by a coil, positioned on the patient's scalp, inducing nerve stimulation within the brain. Current magnetic stimulation techniques and coils are suitable for superficial stimulation of brain, whereas for some medical indications, deeper stimulation would be essential. As superficial stimulation does not induce effective stimulation in the prefrontal cortex (which lays 3-4 cm in depth) and other reward and mood-related brain structures such as the nucleus accumbens (ventral striatum), it may be predicted that deeper brain stimulation may be more effective for the treatment of major depression and other psychiatric and neurological disorders such as autism, post-traumatic stress disorder (PTSD), addictive behaviors including smoking, overeating and drug addiction, schizophrenia, Parkinson's disease, and others. Stimulation of deep brain regions requires a very high intensity which cannot be reached by the magnetic stimulators available today, using standard circular, figure-eight or Double Cone coils without causing undesirable side effects, such as, for example, epileptic seizures or other problems associated with over-stimulation of cortical regions.
A novel approach to TMS has been previously described in International Publication Number WO 02/32504, wherein deep brain stimulation is made possible while minimizing side effects. The device described therein includes a base and an extension portion, the base having individual windings for individual paths of current flow, and the extension portion designed so as to minimize unwanted stimulation of other regions of the brain.